Hemostasis of bleeding or potentially bleeding tissues is of premium importance in open or laparoscopic surgery. Several methods are currently used to coagulate tissues to achieve the desired hemostasis. Sutures are safe, reliable, and commonly used on larger vessels or structures, but are difficult to use on small vessels or structures or in situations involving diffuse bleeding. Monopolar electrosurgery works by electrically heating and burning the tissue to achieve coagulation. It is effective on the smaller vessels and structures but may cause undesirable thermal trauma to adjacent tissues due to stray electrical conduction in a wet surgical environment. Bipolar electrosurgery also works by electrically heating the tissues and provides improved control of stray electrical conduction relative to monopolar electrosurgery. Bipolar instruments may suffer from tissue adherence to the electrodes, causing the coagulated tissue to be re-opened and bleed again as the probes are removed. Ultrasonic instruments use frictional heat generated by rapid vibration rubbing of the tissue to create hemostasis.
Ultrasonic surgical devices for cutting and coagulation of tissue are known. All of these devices utilize longitudinal vibrations in an ultrasonic member to accomplish a desired surgical effect such as cutting with simultaneous coagulation. Clamping mechanisms have been disclosed which claim to improve cutting and coagulation performance by enhancing the tissue contact between the vibrating member and the clamp surface. U.S. Pat. Nos. 3,862,630 and 3,636,943, both to Balamuth, disclose two types of ultrasonic surgical devices: a first device for simultaneously cutting and coagulating tissue, and a second device for joining together layers of tissue. The device for joining together layers of tissue has a vibrating ultrasonic member and a clamp mechanism, the working surface of the clamp mechanism being perpendicular to the direction of the longitudinal vibrations of the tool, so that tissues are compressed between the working surface of the clamp and the end surface of the vibrating ultrasonic member. This “end-on” design blocks tissue access to the clamped region between the ultrasonic member and clamp mechanism from the axial direction, requiring that tissue be accessed laterally, and thereby severely limits application of the device for surgical application because tissue cannot be accessed in a scissor-like fashion.
U.S. Pat. No. 5,322,055 to Davidson discloses an ultrasonic surgical device for simultaneously cutting and coagulating tissue having a vibrating ultrasonic member and a clamp mechanism, the ultrasonic member having a surgical blade with an elongated edge parallel to the axis of longitudinal vibration at the distal end of the vibrating ultrasonic member. This patent alleges enhanced cutting performance due to the surgical blade with the elongated edge and also improves performance by providing tissue access to the ultrasonic member and the clamp mechanism from the axial direction. The clamp mechanism is designed to close completely (i.e., touch) against the vibrating ultrasonic member to achieve the described cutting and coagulation effects. The improved cutting action in this design is allegedly caused by the vibration of the surgical blade with an elongated edge and the complete closure of the blade against the clamp mechanism.
U.S. Pat. No. 6,193,709 to Manna discloses an ultrasonic surgical device for simultaneously cutting and coagulating tissue having a vibrating ultrasonic member and a clamp mechanism, the ultrasonic member having a blade at the distal end of the vibrating ultrasonic member, the blade forming an acute angle with respect to the axis of longitudinal vibration. The patent alleges that the angled design enhances tissue contact between the clamp mechanism and the blade during operation and thereby improves performance. The clamp mechanism is designed to close completely (touch) against the vibrating ultrasonic member to achieve the described cutting and coagulation effects. Improved cutting action in this design is due to the vibration of the blade with the acute angle with respect to the axis of longitudinal vibration and the complete closure of the blade against the clamp mechanism.
U.S. Pat. No. 6,193,709 to Miyawaki discloses an ultrasonic surgical device for treatments such as incision and coagulation having a vibrating ultrasonic member and a clamp having a follow-up mechanism so that the clamp can follow a deflective displacement of the distal end portion of the vibrating ultrasonic member. This patent asserts that the follow-up mechanism eliminates potential gaps between the vibrating ultrasonic member and the clamp mechanism as the clamp mechanism is closed onto the vibrating ultrasonic member, thereby improving grasping and treatment performance. The clamp mechanism is designed to close completely (i.e., touch) against the vibrating ultrasonic member to achieve the described treatments such as incision and coagulation.
None of the patents discloses a device for limiting the closure of the clamp mechanism relative to the vibrating ultrasonic member for the purpose of creating a predetermined clearance there between so that an improved coagulation effect is achieved. Holding the clamp against the ultrasonic member in the prior art devices will inevitably result in the cutting of the tissue. The surgeon has no way of knowing how far the process has occurred from the intended coagulation to undesirable cutting. Indeed, these prior art devices are designed to achieve simultaneous cutting and coagulation as the clamp closes completely against the vibrating ultrasonic member, regardless of the shape of the jaw surface of the clamp mechanism and the shape of the vibrating ultrasonic member. It is often desirable in the course of surgery to coagulate tissue without cutting. It is impossible to reliably separate these two processes in the prior art devices. Thus, there is a need to improve the coagulation performance of ultrasonic surgical devices and further to provide independent cutting and coagulation capabilities.
Deficiencies in the performance of prior art coagulation devices have been noted in the literature. (See, for example, Spivak H. et al., “The Use of Bipolar Cautery, Laparsonic Coagulating Shears, and Vascular Clips for Hemostatis of Small and Medium-sized Vessels,” Surgical Endoscopy, 12(2):183-85 (February 1998) and Landman, J. (Washington University), “Comparison of the Ligasure System, Bipolar Electrosurgery, Harmonic Scalpel, Titanium Clips, Endo-GIA, and Sutures for Laparoscopic Vascular Control in a Porcine Model,” presented at the Society of American Gastrointestinal Endoscopic Surgeons, St. Louis, Mo., (Apr. 10-21, 2001). Both of these studies included the ultrasonic laparosonic coagulating shears (“LCS”) manufactured and distributed by Johnson & Johnson using technology believed to be covered by the Davidson '055 Patent referenced above. Spivak et al. tested the capability of the LCS device and others to coagulate small and medium sized blood vessels in pigs by increasing the associated blood pressure to the point of failure or a maximum load of 300 mm. Hg. While the authors personally concluded that the devices “can be considered safe,” the devices were not uniformly successful. The LCS device was successful in all of the “small vessel” tests but had two complete failures in the twelve tests of medium-sized vessels and two additional instances where the medium-sized vessel commenced bleeding before the defined pressure limit was reached. This is an unacceptable failure rate of 33%. As noted by the authors, the LCS needs to be properly sized and the surgeon properly trained in order to use the LCS successfully on medium-sized vessels. In addition, the authors recommended that “the surgeon have a good alternative method in case initial hemostasis fails.” Similarly, Landman compared various modalities for sealing vessels. On arteries, the LCS succeeded 5/6 times for an 83% success rate; on veins the LCS succeeded 3/6 times for a 50% success rate. Thus, there is clearly a need for significant improvement in a surgical coagulation device.
A means to substantially improve the coagulation performance of ultrasonic surgical instruments has now been discovered. First, the coagulation performance can be improved by separating the coagulation and cutting functions of the instrument so that they are done sequentially rather than simultaneously. Indeed, it has proven helpful to perform the coagulation prior to the cutting rather than simultaneously or in the opposite order. A sequential approach allows time for the tissue to be coagulated and cooled so that it sets before any cutting action occurs. Indeed, tissue bleeding may be totally avoided in this manner. The present invention accomplishes the sequential coagulating and cutting steps with a single grasp of the instrument, meaning that the tissue grasp does not have to be released to alter the instrument for cutting purposes once coagulation is achieved. Second, the coagulation performance is substantially improved by providing a predefined clearance between a jaw surface and a vibrating ultrasonic applicator so that a tissue flow will occur in a carefully controlled manner. The “tissue flow” (i.e., the propensity of the tissue to move plastically upon sufficient heating) in the predefined clearance creates a zone of coagulated tissue that is much less likely to re-bleed than tissue that is simultaneously cut and coagulated with previously disclosed methods. It has now been discovered that if the predefined clearance is carefully controlled to be between about 0.075 to about 1.9 millimeters, and preferably between about 0.075 and about 0.75 millimeters, then the most effective coagulation performance is obtained. It has been found that if the predefined clearance is less than about 0.075 mm, simultaneous cutting action may occur. If the predefined clearance is greater than about 1.9 mm, it has been found that insufficient tissue flow is achieved and complete coagulation may not occur.